Strange occurance with progressive lens!

**smithaboc** · 12-29-2004, 11:35 PM

I'm hoping some of my fellow opticians out there have seen this in a progressive lens!

I have a patient who was prescribed with a plano power progressive lens in his left eye. His right eye has just a little plus power in it, but that eye is not the issue as he doesnt notice the following in this eye. His vision is great and he likes how the progressive works. HOWEVER, he tried to explain to me that in the distance portion of his left eye, the plano power, he notices certain lights are doubled. He explained that, especially at night with an oncoming headlight, he would see the same point of light doubled. Again, it's only in that left eye...there is no issue with prism imbalance or anything to that nature. I could not see what he was saying and I even cut him another lens just to satisfy.

The second lens...same thing! Frustrated he stepped outside the store for a moment and then returned. He brought me outside the store and told me to look through just the left lens in the distance portion and pointed to a halogen type light down the walkway. I had to move the lens in and out just a little bit, but sure enough I could now see what he meant! It was like the same light had a second image displaced just above it and almost forming a pyramid shape distortion of that light.

I even tried a different design progressive but it is doing the very same thing! I am wondering if A/R will take that ghost type image of light away, but I don't understand why it is doing that on just the plano lens and not on the lens with a little bit of power in it.

Has anyone else seen this or can provide me with a little insight as to what is causing this? If you need further info I will provide. I want to be able to offer this patient an explanation! Thanks for your help!

Jaron

**drk** · 12-30-2004, 10:50 AM

If it's occuring in multiple lenses and multiple designs, you can assume it's normal.

It's got to be an internal reflection. Why only in the plano eye? Not sure, but curvature difference may be why. Are they semi rimless or rimless, by chance?

AR has to be helpful here. Put it on and see if it helps.

**Spexvet** · 12-30-2004, 10:59 AM

I wonder if a different base curve would change the relationship of the lens surfaces just enough eliminate the problem. Or more/less face form or pantoscopic tilt.

**eromitlab** · 12-30-2004, 09:56 PM

I believe drk is right about the problem stemming from an internal reflection. I've noticed on some lenses that I wear, sometimes a second "ghosted" point of light appears in the lens near or around the "real" point. It seems more noticeable in Poly and HIP materials as the lenses will tend to have more internal reflections, which is usually counteracted with A/R coats (even they don't totaly clear it up, I still see a violet point around street lamps). My guess would be the plano lens may just be exacerbating the problem of the reflection b/c of the close relation of the front and back curvatures at the distance portion. Rimlon and rimless will only make it worse, especially if they're edge polished.

I don't know if there is a solution other than take him out of progressives and just do readers, or just to deal with it. Honestly, if the distance script is really not much for the other eye (and his reading add isn't a whole lot, say +1.50), this chap might not be an ideal candidate for progressives, IMHO.

**Elmer** · 12-30-2004, 10:31 PM

this has to be a gost image ,this is caused by light reflecting off the back surfacf ot the lens making a zig zag and some of the lmage going through the
lens thus agost image ar will help a lot

**Fezz** · 12-31-2004, 05:04 AM

Ah, the phantom ghost image may be present! Seems to be most noticed in very low powers. I would try more face form and pantoscopic tilt. If this fails, try AR coting and maybe alter the base curve slighty. Good luck.

Fezz
:cheers:

**smithaboc** · 12-31-2004, 10:02 AM

Thank you so much for all the feedback back so far. We are going to try A/R coating and slightly alter the base, then work with panto and face form if the need be. I'll keep everyone posted on the outcome. Thanks again, more suggestions welcome! Jaron

**Rich R** · 12-31-2004, 10:32 PM

I've experienced this a few times through the years, mostly on low power sv lenses though. What seems to work is grinding about .5 prism up in both eyes, I don't really know why this works, it was something Dr. John Archer came accross and it seems to work everytime.

Regards. Rich R

**Monty Scheadler** · 01-13-2006, 04:43 PM

After years of dispencing & surface/finishing PAL's since the first Essilors SNL
I have seen it all. Proper panto and an adjustment geared towards a more "active" lifestyle rather than a desk use could be the cure.

At low additions the is little usable add in the corridor for many designs.

Possibly put him in an Office/Desk design for his work.

Monty

**jtart2** · 01-13-2006, 05:39 PM

The only time I have seen this is when Prism Thinning is ground into the lens.
Take out the Prism and the problems will probably go away!

**JerryR** · 01-13-2006, 07:44 PM

This effect can come about in low powers because of prism thinning. I have plano distance and experience it whenever my progressive has been prism thinned, I do not experience it when lenses are not prism thinned.

**William Stacy O.D.** · 01-13-2006, 09:02 PM

There is no question that it is the prism with low power. Prism always causes a ghost image to be displaced by the amount of the prism, and it's more noticeable in low powers because the ghost is approx. the same size as the main image, and because people who normally wear plano or close to plano powers aren't accustomed to seeing ghosts. (Actually, a plano lens has a BIG ghost, but without prism, it's superimposed on the main image, so you don't see it). But if there were no PRESCRIBED prism, why in hell would a lab grind "thinning prism" in a PLANO LENS???? Stupid. That's one reason I RARELY ALLOW thinning prism in my Rxs. I hate to have to specify "NO THINNING PRISM, THANKS".

Remember, always think out of the box...

**drk** · 01-14-2006, 10:58 AM

Good call, Dr. Stacy.

Can you try to expound on why this happens? Why does a prism cause a ghost image? Is it dispersion? Reflection? Thanks in advance.

**William Stacy O.D.** · 01-14-2006, 11:09 AM

Originally Posted by drk

Good call, Dr. Stacy.

Can you try to expound on why this happens? Why does a prism cause a ghost image? Is it dispersion? Reflection? Thanks in advance.

Actually the prism doesn't cause it, it just moves it or shifts it to a location other than the main image. It is caused by internal reflections, and in low powers these internal reflections are nearly the same size as the original image, so can be very noticeable. In higher powers, the size of the ghost image is smaller or larger than the main image, so is less noticeable. The main ghost image, which is present on all optical lenses, is caused by light passing through the front surface, reflecting back off the second surface towards the first, then reflecting back toward the viewer off the front surface.

**QDO1** · 01-14-2006, 11:39 AM

the prism increases the angle of the internal reflection by 1/2 that of the apical angle of the prism. this moves the two images from the front surface internal reflection, and the rear surface external reflection away from eachother. normally on lower powers the lens is thin, and the images are very close to eachother. The higher the power of the lens, or prism, the larger the deviation

AR coating will definatally resolve this problem.

removal of prism thinning will certainly ensure that the distance portion of the lens will have a reduced image separation between the internal and externally reflected immages, but consequently, as a reduction of prism thinning, the near part of the lens will (because it is becoming more curved) exhibit more of the problem. It is useful to visualise and know the actual lens powers here. they are not putting 6 base up prism on a + 1.25 add!

**William Stacy O.D.** · 01-14-2006, 01:32 PM

Originally Posted by QDO1

the prism increases the angle of the internal reflection by 1/2 that of the apical angle of the prism. this moves the two images from the front surface internal reflection, and the rear surface external reflection away from eachother.

I think the problem is not with two separate reflected images, but with one internally reflected image plus the main (refracted) image. Obviously, a direct reflection off the inside surface, what you are referring to as the "rear external reflection) can add a third image. However, this image is NOT of, say an oncoming headlight. That is always the ghost image (caused by the first order internal reflections). The direct reflection is usually of the patient's own eye, or of a light coming from behind the wearer, and I think not affected by prism.

**QDO1** · 01-14-2006, 01:37 PM

Originally Posted by William Stacy O.D.

I think the problem is not with two separate reflected images, but with one internally reflected image plus the main (refracted) image. Obviously, a direct reflection off the inside surface, what you are referring to as the "rear external reflection) can add a third image. However, this image is NOT of, say an oncoming headlight. That is always the ghost image (caused by the first order internal reflections). The direct reflection is usually of the patient's own eye, or of a light coming from behind the wearer, and I think not affected by prism.

an excelent point - and a good reason for AR coating